docs: def _subspan(self, s, span, nextspan):
          """Recursively subdivide spans based on a series of rules."""
  
          # Split on boundaries between greek and non-greek
          text = s[span[0]:span[1]]
          for i, char in enumerate(text):
              if i < len(text) - 1:
                  nextchar = text[i + 1]
                  if (char in GREEK and nextchar not in GREEK) or (char not in GREEK and nextchar in GREEK):
                      return [(span[0], span[0] + i + 1), (span[0] + i + 1, span[1])]
  
          # Perform all normal WordTokenizer splits
          return super(FineWordTokenizer, self)._subspan(s,span, nextspan)